Insertion cannulae are used to produce openings in the skin for the insertion of various medical devices into soft tissue or organs. For example an insertion cannula can be inserted through a needle puncture and a catheter can then be inserted by means of the cannula through the skin into the patient. After insertion of the catheter the cannula is removed from the patient again. In general terms in that respect the catheter is connected to a medical unit before the cannula is removed. In order to permit withdrawal of the cannulae in the proximal direction in spite of obstacles such as electrode plugs or catheter connections the cannula in the withdrawal operation is simultaneously torn open or cut open by means of a cutting tool which is disposed in proximal relationship.
U.S. Pat. No. 4,377,165 discloses a separable introduction device (“introducer”). That device has at a long side a desired-rupture location along which the introduction device can be severed for the removal thereof. In that case the desired-rupture location can be for example in the form of a notch, a perforation, holes or the like.
In that respect however it has been found that there is the disadvantage that the stability of the introduction device is reduced in order to provide the possibility of cutting open the introduction device. For example by virtue of its reduced stability the introduction device can be severed easily and at the wrong moment in time. Undesired severing of the introduction device can occur for example if the device is firstly introduced into the patient before the catheter has been completely inserted into the patient through the introduction device, before the catheter has been connected to the desired medical unit or before the introduction device has been removed from the patient and from the catheter.
In addition the above-described severable introduction device does not afford reliable severing and has a tendency to suffer from sharp edges when it is severed.
U.S. Pat. No. 5,752,937 discloses a medical introduction device. In that case the introduction device has a tube with a reinforcing strip or a wire which are let into the material of the tube and which extend substantially along the longitudinal axis of the tube. In that arrangement the reinforcing strip or the wire can be made from any suitable material which can be used as a cutting means which can be pulled along the longitudinal axis of the tube in order to cut open the introduction device and thereby to sever the introduction device for removal from the catheter. The reinforcing strip or the wire in that case presents a greater shearing force than the material of the tube of the introduction device. The operation of cutting open the introduction device by the reinforcing strip or the wire is effected by virtue of the difference in the levels of shearing strength.
That arrangement however has been found to suffer from the disadvantage that the entire longitudinal wall of the tube of the introduction device has to be cut through simultaneously.
Therefore the problem of the invention is to provide a device for implanting catheters, which can be easily cut open upon removal from the body without in that respect neglecting the necessary stability requirements.